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Vulnerabilities

Vulnerability · CVE-2026-21921

A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges

Published Jan 15, 2026 · catalog updated Jan 15, 2026 · Juniper Networks Junos OS

Last checked Oct 30, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-21921. EPSS is 0.37%. Act only if a listed version of Juniper Networks Junos OS is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High7.1
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.37%
Remediation
Version ranges on file
Affected products
vendor Juniper Networks Junos OS 23.4 <23.4R2

A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges to cause a Denial-of-Service (DoS). When telemetry collectors are frequently subscribing and unsubscribing to sensors continuously over a long period of time, telemetry-capable processes like chassisd, rpd or mib2d will crash and restart, which - depending on the process - can cause a complete outage until the system has recovered. This issue affects: Junos OS: * all versions before 22.4R3-S8, * 23.2 versions before

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor Juniper Networks Junos OS 23.4 <23.4R223.4 <23.4R2

How to fix CVE-2026-21921

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-21921. EPSS is 0.37%. Act only if a listed version of Juniper Networks Junos OS is installed.

Which versions are affected?

Compare what you have installed with Juniper Networks Junos OS 23.4 <23.4R2 23.4 <23.4R2. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.37%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Juniper Junos OS security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jan 15, 2026 · EUVD

    Detected

    A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges to cause a Denial-of-Service (DoS). When telemetry collectors are frequently subscribing and unsubscribing to sensors continuously over a long period of time, telemetry-capable processes like chassisd, rpd or mib2d will

  2. Jan 15, 2026 · EUVD

    Updated

    A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges to cause a Denial-of-Service (DoS). When telemetry collectors are frequently subscribing and unsubscribing to sensors continuously over a long period of time, telemetry-capable processes like chassisd, rpd or mib2d will

Sources

  • CVE.orgVulnerability recordCVE-2026-21921

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-21921

    30-day exploitation probability 0.37%

    first.org
  • EUVDVulnerability recordEUVD-2026-2693

    A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges to cause a Denial-of-Service (DoS). When telemetry collectors are frequently subscribing and unsubsc

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Oct 30, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • CVE.orgOct 30, 2026
  • FIRST EPSSOct 30, 2026
  • EUVDOct 30, 2026